1. Field of the Invention
The present invention relates to a circuit for controlling a timing of overdriving an internal voltage of a memory device, and more particularly to, a circuit for controlling a timing of overdriving a core voltage which is a driving voltage of a sense amplifier of a memory device and a duration of the overdriven core voltage.
2. Description of the Related Art
In general, a memory device is driven by an external power voltage Vext, but internal circuits of the memory device are driven by various levels of internal voltages generated in internal voltage generators of the memory device. Therefore, the levels of the internal voltages must be stabilized to improve the operation of the memory device.
Especially, the read/write operations are major functions of the memory device. It is thus essential to stabilize a core voltage which is one of the internal voltages used for the read/write operations. Here, the core voltage implies an internal voltage used as a driving voltage of a sense amplifier during the read/write operations.
In the auto refresh operation, the read/write operations are performed on a number of memory cells at the same time, which may increase transient current consumption and destabilize the level of the core voltage. Because variations of the core voltage affect the performance and reliability of the memory device, a compensation circuit for restricting rapid variations of the core voltage is generally provided.
FIG. 1 is a circuit diagram illustrating a general core voltage generator.
Referring to FIG. 1, a core voltage driver 101 outputs a core voltage Vcore, and a core voltage over-driver 102 restricts variations of a level of the core voltage Vcore during the operation of a sense amplifier. That is, while the sense amplifier is operated, the core voltage over-driver 102 couples an externally-supplied driving voltage VDD to a core voltage terminal, thereby compensating for power.
A driving timing of the core voltage over-driver 102 is very important. When the core voltage over-driver 102 is operated much earlier or later than the sense amplifier, effects of the core voltage over-driver 102 are reduced.
In addition, how long the core voltage over-driver 102 is operated is also very important. When the core voltage over-driver 102 is operated for an extended period of time, the core voltage Vcore unnecessarily rises.
However, a circuit for precisely monitoring and tuning an operation timing of the core voltage over-driver 102 has not been suggested. It is thus difficult to output stable internal voltages.
Furthermore, after a packaging process of a semiconductor device is finished, the internal voltages of the semiconductor device cannot be externally measured.